LAPACK  3.6.1
LAPACK: Linear Algebra PACKage
subroutine dswap ( integer  N,
double precision, dimension(*)  DX,
integer  INCX,
double precision, dimension(*)  DY,
integer  INCY 
)

DSWAP

Purpose: 
    interchanges two vectors.
    uses unrolled loops for increments equal one.
Author
Univ. of Tennessee
Univ. of California Berkeley
Univ. of Colorado Denver
NAG Ltd.
Date
November 2011
Further Details: 
     jack dongarra, linpack, 3/11/78.
     modified 12/3/93, array(1) declarations changed to array(*)

Definition at line 53 of file dswap.f.

53 *
54 * -- Reference BLAS level1 routine (version 3.4.0) --
55 * -- Reference BLAS is a software package provided by Univ. of Tennessee, --
56 * -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..--
57 * November 2011
58 *
59 * .. Scalar Arguments ..
60  INTEGER incx,incy,n
61 * ..
62 * .. Array Arguments ..
63  DOUBLE PRECISION dx(*),dy(*)
64 * ..
65 *
66 * =====================================================================
67 *
68 * .. Local Scalars ..
69  DOUBLE PRECISION dtemp
70  INTEGER i,ix,iy,m,mp1
71 * ..
72 * .. Intrinsic Functions ..
73  INTRINSIC mod
74 * ..
75  IF (n.LE.0) RETURN
76  IF (incx.EQ.1 .AND. incy.EQ.1) THEN
77 *
78 * code for both increments equal to 1
79 *
80 *
81 * clean-up loop
82 *
83  m = mod(n,3)
84  IF (m.NE.0) THEN
85  DO i = 1,m
86  dtemp = dx(i)
87  dx(i) = dy(i)
88  dy(i) = dtemp
89  END DO
90  IF (n.LT.3) RETURN
91  END IF
92  mp1 = m + 1
93  DO i = mp1,n,3
94  dtemp = dx(i)
95  dx(i) = dy(i)
96  dy(i) = dtemp
97  dtemp = dx(i+1)
98  dx(i+1) = dy(i+1)
99  dy(i+1) = dtemp
100  dtemp = dx(i+2)
101  dx(i+2) = dy(i+2)
102  dy(i+2) = dtemp
103  END DO
104  ELSE
105 *
106 * code for unequal increments or equal increments not equal
107 * to 1
108 *
109  ix = 1
110  iy = 1
111  IF (incx.LT.0) ix = (-n+1)*incx + 1
112  IF (incy.LT.0) iy = (-n+1)*incy + 1
113  DO i = 1,n
114  dtemp = dx(ix)
115  dx(ix) = dy(iy)
116  dy(iy) = dtemp
117  ix = ix + incx
118  iy = iy + incy
119  END DO
120  END IF
121  RETURN